1. Field of the Invention
The present invention relates to a mechanical ground anchor, particularly to a ground anchor that is reusable and that provides a reactive force resistance body when subjected to loading.
2. Description of Background Information
Up to the present, a straddle type of the mechanical anchor is well known as a ground anchor available for such a loading. As one of the straddle type of mechanical anchors, a self-boring type is known as disclosed in Japanese Patent Application No. HEI 4-13496 of the same Applicant where a cylindrical shaped anchor body divided into two parts is connected to a head plate mounted at the bottom end of the drilling rod by using a joint pin. This mechanical anchor is designed so that the anchor body could be straddled taking the form of an inverted V-shape by means of a jack provided in the anchor body when it reaches a certain depth by self-boring. For reasons that such existing mechanical anchor is designed so as to join the anchor body to the head plate by using a pin joint, however, there were the following points at issue:
(1) In the case of such a pin-joint, its structural strength such as a magnitude of its rotational torque and/or tensile strength depends on its section performance such as the length and/or diameter of the pin, while, by reason of the limited structural space of the mechanical anchor, the available size of the pin is limited and its rotational torque and/or tensile strength are restricted as a result. PA1 (2) The magnitude of its rotational torque while being bored remaining straddled depends on the soil foundation hardness and depth to be bored. For this reason, the existing mechanical anchor could not be applied to such hard soil foundation as pebbly stratum and/or extremely deep excavation in many cases of the self-boring. PA1 (3) Tensile strength while the anchor body is applied remaining straddled also depends on section performance of the pin. For this reason, pulling resistance force depending on the soil foundation could not always be maximized. PA1 (4) Because the straddled anchor body takes the form of cylinder divided into two parts that rotate during boring, and due to the condition that only its upper end is joined to the boring rod, the existing mechanical anchor has a weakness during rotary boring. PA1 (5) In collapsible soil foundation, it is often effective to strengthen boring walls by means of injecting a soil stabilizer such as bentonite liquid into the boring wall and then straddle the anchor body. It is, however, impossible to inject such soil stabilizer with the existing mechanical anchor from a structural point of view.